In conventional measuring circuits, such as RMS to DC and peak-to-peak measuring circuits, which respond to input signals whose magnitude varies with respect to time, the useful range of the measuring circuit is limited by its dynamic range. There is disclosed in the above-identified copending U.S. patent application, a technique for extending the useful range of a measuring circuit through the use of an input circuit which establishes the magnitude of an input signal within the defined dynamic range of the measuring circuit and an output circuit which responds to the output signal of the measuring circuit by re-establishing the magnitude at a level corresponding to the magnitude of the initial input signal.
In the invention described below, the output circuit of the above-referenced copending patent application is replaced by a log-ratio circuit which combines with an automatic gain control circuit to both extend the useful range of the measuring circuit and optimize the signal-to-noise ratio performance of the measuring circuit.